In recent years, among color display devices used for image displays in computers and televisions, field emission display panels and plasma display panels (hereafter simply, “PDPs”) have received special attention as display devices that can realize slim-type panels. Particularly, PDPs are advantageous in their rapid responses and wide viewing angles, and so companies and research institutions are engaged in active developments to make PDPs widely available.
A PDP has the following construction. A front glass substrate on which a plurality of line-shaped electrodes are arranged in parallel, and a back glass substrate on which a plurality of line-shaped electrodes are arranged in parallel are arranged opposed to each other with gap members interposed between them, in such a manner that the electrodes on the front panel and the electrodes on the back panel are perpendicular. A discharge gas is enclosed in a space formed between the front and back glass substrates. On the surface of the front glass substrate opposing to the back glass substrate, a dielectric layer is formed to cover the electrodes arranged on the front glass substrate. Further, a protective layer, which is an electron emission thin-film, is formed on the dielectric layer.
The PDP is driven in the following way. An address discharge is performed successively between the electrodes on the front glass substrate and the electrodes on the back glass substrate, generating charge on the protective layer surface of cells in which light emission is intended. Then, a sustained discharge is performed between adjacent electrodes on the front glass substrate relating to the cells in which the charge has been generated.
The protective layer on which charge is generated by an address discharge mainly has two functions. The one function is to protect the dielectric layer and the electrodes against ion bombardment (spattering) occurring at the time of address discharge. The other function is a so-called memory function to retain charge by emitting secondary electrons at the time of address discharge. To realize these functions, magnesium oxide (MgO) that excels in resistance to spattering and in secondary electron emission characteristics is commonly used as a material for the protective layer.
In the field of display devices, demands for higher-definition screens have emerged recently. To meet the demands, higher-definition screens are realized by increasing the number of electrodes per unit area of each substrate and thereby increasing the number of cells.
However, the address time to be spent on one cell becomes shorter as a larger number of electrodes are provided to increase the number of cells. The number of secondary electrons emitted from the protective layer at the time of address discharge decreases accordingly, causing the above-described memory function to be degraded. As a result, such a PDP may suffer from erroneous light emission easily occurring along with generation of an erroneous address discharge. With this background, a technique for improving secondary electron emission characteristics of an MgO thin-film is presently being called for.